The present invention relates to spectrum analysis, and more particularly to an instrumentation receiver using a preselection filter bank and a switched local oscillator counter.
A known instrumentation receiver described in U.S. Pat. No. 6,316,928 incorporates a yttrium-iron-garnet (YIG) tuned oscillator (YTO) as a sweep frequency local oscillator and a YIG tuned filter (YTF) as a frequency preselector for an incoming RF signal. The YTF is used to remove image products in a high frequency band before a first conversion stage. However the YTF has the disadvantages of high cost and limited bandwidth. The architecture disclosed in the '928 patent is a dual-IF architecture having a baseband IF channel and a high-band IF channel both using the same YTO. The baseband IF channel upconverts the RF signal to a first IF frequency, bandpass filters the first IF frequency and downconverts to a second IF frequency. The high-band IF channel preselects a frequency band using the YTF and downconverts directly to the second IF frequency. An input switch allows the RF signal to be processed by either the baseband or high-band IF channel, with a corresponding output switch selecting the selected IF channel for further processing. This architecture provides a two-octave bandwidth from a one-octave YTO rather than using a more expensive two-octave YTO.
What is desired is an instrumentation receiver that has a lower cost while providing a greater bandwidth.